Plasma processing device

Abstract

The objective of the present invention is to provide a plasma processing device that generates an axially symmetrical electric field distribution under a wide range of conditions without actively allowing microwave energy to be lost other than for the generation of plasma, and to enable uniform processing. To this end, the plasma processing device comprises a septum polarizer (15) that allows microwaves that have propagated via a circulator (12) to propagate to a processing chamber, wherein: one port of the circulator (12) is connected to each of one port of the septum polarizer (15) and the other port of the septum polarizer (15), and the other port of the circulator (12) is connected to a high-frequency power supply; and the one port of the septum polarizer (15) is a port for converting the propagated microwaves to right-handed circularly polarized waves, and the other port of the septum polarizer (15) is a port for converting the propagated microwaves to left-handed circularly polarized waves.

Description

Plasma processing equipment

[0001] The present invention relates to a plasma processing apparatus.

[0002] In the manufacture of semiconductor devices, plasma processing equipment is often used for various processes such as etching, film deposition, and cleaning. To achieve the desired processing results, various factors, including pressure and gas species, are adjusted. From the viewpoint of yield, proper control of the plasma distribution within the processing chamber is one of the important factors for achieving uniform processing across the entire wafer surface.

[0003] In the past, in the case of a plasma processing apparatus that uses microwaves to generate plasma, for example, when the TE11 mode, which is the fundamental mode of a cylindrical waveguide, is introduced into the processing chamber as linearly polarized waves, the spatial distribution of electric field strength becomes non-axially symmetric, which can result in non-uniform processing. As a countermeasure, Patent Document 1 proposes a method in which the polarization plane is rotated by using a circularly polarized wave generating means, thereby making the electric field distribution in the processing chamber axially symmetric.

[0004] Japanese Patent Application Laid-Open No. 2006-179477

[0005] Takeshi Fukusako, "Fundamentals of Circularly Polarized Antennas," Corona Publishing, 2018, pp. 110-111

[0006] In a method using a circularly polarized wave generating means, the influence of reflected waves from the processing chamber, whose characteristics vary depending on the process conditions, can cause the circularly polarized wave input to the processing chamber to be mixed with a reverse-rotation component, resulting in an axially elliptically polarized wave, which can degrade the uniformity of the plasma distribution. For this reason, Patent Document 1 also proposes a method of suppressing the effect on uniformity by providing a dummy load to absorb the reflected waves. However, with the method using a dummy load, the reflected portion of the energy that would normally be used to generate plasma is converted into heat, increasing power loss, and there is a concern that a larger power supply will be required to compensate for this.

[0007] An object of the present invention is to provide a plasma processing apparatus that generates an axially symmetric electric field distribution under a wide range of conditions and enables uniform processing without actively losing microwave energy other than through plasma generation.

[0008] The present invention has the following configuration to achieve the above object. The plasma processing apparatus includes a processing chamber in which a sample is plasma-processed, a high-frequency power supply that supplies high-frequency microwave power, a magnetic field forming mechanism that forms a magnetic field in the processing chamber, and a sample stage on which the sample is placed. The plasma processing apparatus further includes a septum polarizer that propagates microwaves propagated through a circulator into the processing chamber, one port of the circulator being connected to one port of the septum polarizer and the other port of the septum polarizer via an impedance matching unit, the other port of the circulator being connected to the high-frequency power supply via a matching box. The one port of the septum polarizer is a port that converts the propagated microwave into a right-handed circularly polarized wave, and the other port of the septum polarizer is a port that converts the propagated microwave into a left-handed circularly polarized wave. The impedance matching unit includes a rectangular waveguide, and the width dimension of the rectangular waveguide and the waveguide length dimension of the rectangular waveguide are specified so that the propagated microwave is impedance-matched.

[0009] Furthermore, the plasma processing apparatus includes a processing chamber in which a sample is plasma-processed, a high-frequency power supply that supplies microwave high-frequency power via a matcher, a magnetic field forming mechanism that forms a magnetic field in the processing chamber, and a sample stage on which the sample is placed, and further includes a Faraday rotator that rotates the phase of the polarization plane of the linearly polarized wave propagated through the matcher by (90×n+45) degrees, where n is an integer, and a waveguide-type circular polarization converter that switches between right-handed and left-handed circular polarization of the outputted circularly polarized wave every time the phase of the polarization plane of the linearly polarized wave rotated by the Faraday rotator changes by 90 degrees, wherein the waveguide-type circular polarization converter is disposed between the Faraday rotator and the processing chamber, and impedance is matched between the Faraday rotator and the waveguide-type circular polarization converter.

[0010] According to the present invention, it is possible to provide a plasma processing apparatus that generates an axially symmetric electric field distribution under a wide range of conditions and enables uniform processing without actively losing microwave energy other than through plasma generation.

[0011] The present invention relates to a plasma processing apparatus and a mode converter, and a circular polarizer according to the present invention.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] FIG. 1 shows a plasma processing apparatus according to an embodiment of the present invention. Microwaves having a frequency of 2.45 GHz are generated by a microwave source 1 such as a magnetron and transmitted through a rectangular waveguide 2 to a mode converter 5 via an isolator 3 and a matching box 4. The microwaves transmitted to the mode converter 5 are further radiated into a cylindrical cavity 7 via a cylindrical waveguide 6, generating plasma in a processing chamber 9 separated by a microwave introduction window 8 below the cylindrical cavity 7. A gas introduction system and a vacuum exhaust system (not shown) are connected to the processing chamber 9, and the interior of the processing chamber 9 is maintained at a gas atmosphere and pressure suitable for processing. A sample stage 11 is provided within the processing chamber 9 for placing a wafer 10, which is the object to be processed.

[0014] At the same time, an electromagnetic coil (not shown) is provided to surround the cylindrical cavity 7 and the processing chamber 9, creating a magnetic field strength surface of 0.0875 tesla, which induces electron cyclotron resonance in the processing chamber 9, thereby forming plasma in the material gas supplied from the gas introduction system described above.

[0015] FIG. 2 shows the details of the mode converter 5. The two openings 20 and 21 of the T-shaped circulator 12, which is closest to the power supply and has a bias magnetic field application unit (e.g., microwave ferrite with a bias magnetic field applied by a permanent magnet) on the waveguide, are connected to the openings of the two E-corners 13a. As can be seen from FIG. 2, the two E-corners 13a are arranged symmetrically. Two E-corners 13b are connected to the bottom of the E-corner 13a in a folded-back manner, and two E-corners 14 are connected to be sandwiched between the E-corners 13a and 13b. The E-corners 13a, 13b, and 14 are collectively referred to as the impedance matching unit.

[0016] A cylindrical waveguide 16 is connected to the lower part (processing chamber side) of the E-corner 14. Inside the cylindrical waveguide 16, a tapered, sloped septum (partition) 15 made of metal is provided. A circular polarizer (cylindrical waveguide) equipped with such a septum (partition) is called a septum polarizer. The diagram on the lower left of Figure 2 is a side view of the septum polarizer so that the shape of the "sloped septum" can be seen.

[0017] Furthermore, two ports (openings) 22 and 23 at the bottom (processing chamber side) of the E-corner 14 are independently connected to two ports (openings) 24 and 25 at the top (power supply side) of the septum polarizer.

[0018] The circulator 12 does not necessarily have to be T-shaped, and may be Y-shaped or the like. Furthermore, the bias magnetic field application unit described above can use an electromagnet (electromagnetic coil) instead of a permanent magnet, allowing the sense of circular polarization, described below, to be electrically switched. It is desirable to select a microwave ferrite material with as low a loss as possible at the frequency to be used. However, since there are already circulators on the market with an insertion loss of approximately 0.1 dB at a frequency of 2.45 GHz, which is sufficiently low loss for practical use, it is sufficient to select one from these.

[0019] Furthermore, in this embodiment, the mode converter 5 has a symmetrical structure, but as long as impedance matching is achieved between the circulator 12 and the septum polarizer, the waveguide lengths of the E-corners 13a and 13b can be determined arbitrarily. Under similar constraints, H-corners, bends, coaxial cables, etc. may be used instead of the E-corners 13a and 13b.

[0020] Here, we will explain septum polarizers. Septum polarizers are known as a means of generating circularly polarized waves, and are described, for example, on page 111 of "Fundamentals of Circularly Polarized Antennas (by Takeshi Fukusako, Corona Publishing, 2018)." While only a stepped septum is described there, in applications other than broadband applications, a simpler shape, such as a sloped septum, can simplify the shape optimization process in the design. Of course, the septum shape can also be stepped or have other shapes, as needed.

[0021] The septum polarizer has properties that allow the sense of circular polarization (the direction of rotation of the electric field, right-handed or left-handed) to be determined depending on which of the two ports separated by the septum the microwave is introduced from. In this embodiment, the polarizer is configured to convert the traveling wave FW from the circulator 12 into right-handed circular polarization. However, the polarizer may also be configured to convert the traveling wave into left-handed circular polarization by inverting either the circulator 12 or the sloped septum 15. The dimensions of each part of the septum polarizer can be determined using known dimensions or electromagnetic field simulation software such as HFSS (full-wave 3D electromagnetic field software).

[0022] The septum polarizer also has the property that the sense of the microwave from the cylindrical waveguide determines which of the ports separated by the septum the microwave propagates to. In this embodiment, the section below the cylindrical cavity 7 has an axially symmetrical structure, so the sense of the reflected wave RW from the processing chamber is inverted relative to the forward wave FW, and the reflected wave RW propagates along the other path, not the path of the forward wave FW. Note, however, that the sense of the circularly polarized wave is defined based on the wave's traveling direction. Furthermore, in general plasma processing apparatuses, the periphery of the processing chamber often has an axially symmetrical structure for uniform processing, and the premise of the axially symmetrical structure described above is not particularly limited to this embodiment.

[0023] Incidentally, the generation of elliptically polarized waves, which was a problem in the prior art, was caused by the reflected microwave RW from the processing chamber 9 being converted into a circularly polarized wave with the opposite sense inside the mode converter 5 and then re-entering, whereby the circularly polarized waves with different senses are mixed and propagated toward the processing chamber. However, in this embodiment, as shown in Figure 2, the reflected microwave RW propagating from the processing chamber to the circulator 12 returns to the power supply side without being re-reflected inside the mode converter 5 (see "Top view of mode converter" in the upper right of Figure 2).

[0024] The microwaves returning to the power supply side are pushed back by the matching box 4 and propagate again as traveling waves FW along the path shown in the figure. Therefore, waves of a different sense than desired are not propagated to the processing chamber side, and deterioration of the uniformity of the electric field distribution due to mixing of waves of different senses does not occur. Furthermore, the components of the mode converter 5 do not include elements such as dummy loads that actively lose microwave energy, and all have sufficiently low loss for practical use, so that the energy can be effectively used to generate plasma.

[0025] However, this assumes that sufficient impedance matching is achieved between the circulator 12 and the septum polarizer. If mismatching causes reflection within the impedance matching sections such as the E-corner 13a, 13b, and 14, the microwave will propagate directly (in the case of the reflected wave RW) or via the circulator 12 (in the case of the traveling wave FW) to the other port above the septum polarizer, generating a circularly polarized wave in the opposite sense. To avoid this, in this embodiment, impedance matching is achieved for the operating frequency of 2.45 GHz by adjusting the width and length of the rectangular waveguide in the E-corner 14.

[0026] In this embodiment, the same effect can be obtained even when a static magnetic field with an axially symmetric distribution is applied to the processing chamber 9, for example, as in an ECR plasma processing apparatus, with a strength sufficient to cause electron cyclotron resonance. In this case, the anisotropy of the dielectric constant of the magnetized plasma causes the reflection characteristics from the processing chamber to change depending on the sense of circular polarization. Although the magnitude of the reflection may change depending on the sense, the fact remains that when the traveling wave FW is right-handed circularly polarized, the reflected wave RW is left-handed circularly polarized, and vice versa, regardless of the anisotropy. Therefore, the uniformity effect of this embodiment can also be obtained in an ECR plasma processing apparatus.

[0027] Further advantages of this embodiment include that there is virtually no response time because the system configuration is simple without using a feedback control system, and that there is no need for moving parts such as an electric field sensor for monitoring the axial ratio of the circularly polarized wave (an index of the degree of sense mixing) or an actuator for adjusting the characteristics of the mode converter 5.

[0028] Another embodiment of the mode converter 5 will now be described. Fig. 3 shows the structural details of the mode converter 5 according to the second embodiment. The microwaves from the matching box 4 are bent vertically by a square-to-circular converter 32 while preserving the angle of the polarization plane (a plane parallel to the propagation direction and the electric field direction), and are then propagated to a Faraday rotator 33. The Faraday rotator 33 is a stepped cylindrical waveguide 37 equipped with a ferrite rod 34 and its support 35 inside, and an external coil 36 for applying a bias magnetic field to the ferrite rod 34, and rotates the polarization plane of the linearly polarized wave by 45° in a right-handed screw direction facing vertically downward by the Faraday effect. The quarter-wave plate 38 arranged inside the cylindrical waveguide 39 is made of a quartz plate with rectangular notches cut out from the top and bottom of a rectangular parallelepiped, as shown in the right diagram of FIG. 3, and is arranged so that its long side, as seen from above, is tilted by an additional 45° with respect to the plane of polarization, as will be explained in FIG. 4, and converts the linearly polarized wave from the Faraday rotator 33 into a (clockwise) circularly polarized wave.

[0029] Figure 4 shows the state of polarization at each part of the mode converter 5. First, the left diagram in Figure 4 will be explained. The traveling wave FW converted from the TE10 mode of the rectangular waveguide to the TE11 mode of the cylindrical waveguide by the square-circular converter 32 has an electric field in the direction of polarization P1a above the Faraday rotator 33. After that, the FW transmitted through the ferrite rod 34 biased by a vertically downward DC magnetic field is rotated by 45° in the vertically downward right-hand screw direction by the Faraday effect, and the direction of the electric field above the quarter-wave plate 38 becomes P2a.

[0030] The quarter-wave plate 38 converts the microwave into a right-handed circularly polarized wave (P3a) because the long side of the quarter-wave plate 38, viewed from above, is angled 45° with respect to P2a in a right-handed screw direction pointing vertically downward. Here, the microwave is defined as being right-handed (right-handed) if the electric field is clockwise when facing the direction of propagation of the microwave, and as being left-handed (left-handed) if it is counterclockwise. The FW propagating downward from the quarter-wave plate 38 has a portion of its power reflected below the boundary (load) between the cylindrical waveguide 6 and the cylindrical cavity 7, and returns to the mode converter 5 as a reflected wave (RW), as shown in the right diagram of Figure 4.

[0031] Here, if the load is geometrically sufficiently axially symmetric as in this embodiment, when FW is a circularly polarized wave, RW also becomes a circularly polarized wave, and further, when FW is right-handed, RW becomes left-handed, and when FW is left-handed, RW becomes right-handed, that is, the sense (the direction of rotation of the electric field) is reversed, that is, they become cross-polarized waves. Note that in general plasma processing apparatuses, it is common to design the processing chamber to be axially symmetric in order to achieve uniform processing, so the above assumption does not particularly hold true in this embodiment.

[0032] The RW, now a left-handed circularly polarized wave (P3b), passes through the quarter-wave plate 38 again and is converted back into a linearly polarized wave. At this time, the RW polarization P2b at the top of the quarter-wave plate 38 also becomes a cross-polarized wave perpendicular to P2a. The RW is then subjected to Faraday rotation by the ferrite rod 34. Due to the nature of Faraday rotation, whether it rotates clockwise or counterclockwise is determined based on the direction of the bias magnetic field, not the direction of propagation of the microwave. That is, while the FW tilts clockwise when viewed in the direction of propagation of the microwave, the RW tilts counterclockwise when viewed in the direction of propagation of the microwave (it always tilts in the direction of a right-hand screw relative to the direction of the bias magnetic field). Therefore, the direction of the RW polarization P1b at the top of the ferrite rod 34 coincides with P1a. This polarized wave can be transmitted without being reflected again by the square-to-circular converter 32 and propagated to the matching box 4.

[0033] Let us consider a case where there is no Faraday rotator 33. In this case, RW and FW have planes of polarization P2a and P2b that differ by 90° from each other below the rectangular-circular converter 32. Furthermore, since the rectangular-circular converter 32 preserves the polarization angle of the microwaves that pass through it, RW tries to propagate through the rectangular waveguide 2 as the TE01 mode with a horizontal polarization plane.

[0034] However, in order to facilitate handling of microwaves in the microwave source 1, isolator 3, and matching box 4, the rectangular waveguide 2 is usually designed to have standard dimensions that allow only the fundamental mode TE10 of WR-430 or the like to propagate when the frequency is 2.45 GHz, and the higher-order mode TE01 cannot propagate through the rectangular waveguide 2. Therefore, RW is entirely re-reflected by the rectangular-circular converter 32 and re-enters the chamber as a secondary traveling wave FW'.

[0035] The preservation of the polarization plane by the rectangular-circular converter 32 holds even when reflected, and the polarization plane of FW' remains perpendicular to RW above the quarter-wave plate 38. Therefore, FW' converted into circular polarization below the quarter-wave plate 38 has the opposite sense to FW. A state in which circularly polarized waves of different senses are superimposed in the same traveling direction is called an elliptical polarization because the electric field vector traces an elliptical orbit, and the axial symmetry of the electric field distribution of an elliptical polarization decreases as the degree of sense mixing increases. In other words, without the Faraday rotator 33, the FW' increases as the RW / FW ratio (reflection coefficient) increases, and the axial symmetry decreases because the degree of sense mixing increases.

[0036] On the other hand, when the Faraday rotator 33 is present, the FW' is absent or sufficiently small, thereby suppressing the effect of the RW / FW ratio on the symmetry. The RW / FW ratio varies depending on the configuration of the cylindrical cavity 7, microwave introduction window 8, processing chamber 9, etc., as well as on processing conditions such as the gas used in processing, the pressure in the processing chamber, and the power of the microwaves input. In other words, the fact that the axial symmetry of the electric field distribution generated by the mode converter 5 does not depend on the RW / FW ratio enables uniform processing under a wider range of conditions.

[0037] In the absence of the Faraday rotator 33, part of the FW' is reflected from the load as RW', just like the FW, but since the polarization plane angle of the RW' matches that of the FW in the rectangular-circular converter 32, it can return as a TE10 mode through the rectangular waveguide 2 to the matching box 4. Therefore, the RW' does not affect the axial symmetry of the electric field distribution in the processing chamber.

[0038] The above discussion is based on the premise that there is no or sufficiently small reflection of microwaves at the interface between the Faraday rotator 33 and the quarter-wave plate 38, i.e., impedance matching is achieved. If this premise is not also met in the above discussion, the axial symmetry of the electric field distribution will ultimately change depending on the RW / FW ratio.

[0039] Therefore, in this embodiment, to satisfy this premise, a cylindrical stepped waveguide 37 is used for the Faraday rotator 33, and the diameter and length of the steps are adjusted to minimize the reflection at the interface at the power supply frequency used. The outer diameter, thickness, and dimensions of the upper and lower notches of the quarter-wave plate 38 are also adjusted in the same way.

[0040] In order for the mode converter 5 to efficiently transmit microwave power to the processing chamber, internal losses must be minimized. Therefore, a low-loss material, such as a garnet-type ferrite based on YIG (yttrium iron garnet), is used for the ferrite rod 34. Furthermore, PTFE, which has a low dielectric loss tangent, is used for the support 35. The ferrite rod 34 and support 35 are fixed by press-fitting, but if fixed with an adhesive, it is preferable to use an adhesive with a low dielectric loss tangent, such as a polyimide adhesive. Furthermore, when using high power, care must be taken not only to ensure power efficiency but also to ensure that heat generated does not exceed the Curie temperature of the ferrite rod 34. If the allowable temperature is exceeded, an additional cooling mechanism may be required.

[0041] Cylindrical waveguide 39 with quarter-wave plate 38 is generally a type of "waveguide polarizer" (see Non-Patent Document 1), but all waveguide polarizers, like the configuration of this embodiment, have the property that when converting linearly polarized wave to circularly polarized wave, if the electric field direction of the linearly polarized wave differs by 90°, the sense of the output circularly polarized wave is reversed, and conversely, when converting circularly polarized wave to linearly polarized wave, the electric field direction of the output linearly polarized wave changes by 90° depending on the sense of the input circularly polarized wave. Therefore, the same effect can be obtained using any waveguide polarizer, not just the configuration of this embodiment.

[0042] As described above, this embodiment utilizes the fact that, by setting the rotation angle of the Faraday rotator 33 to 45°, waves that have passed twice in both directions are rotated by a total of 90°. More generally, if the Faraday rotation angle θ = 90° × n + 45° (n is an arbitrary integer), waves that have passed twice in both directions through the Faraday rotator 33 are rotated by a total of 2θ = 180° × n + 90°. Here, because the plane of polarization remains unchanged for a rotation of 180° × n, the same effect can be obtained for any n. However, in order to increase the absolute value of the rotation angle, modifications such as increasing the length of the ferrite rod 34 are necessary. Therefore, unless there is a special reason, it is desirable from a design perspective to set |θ| = 45°.

[0043] Right-handed and left-handed circularly polarized waves have the same axial symmetry of the electric field. Therefore, in this embodiment, the quarter-wave plate 38 may be rotated 90° about the vertical axis to convert the circularly polarized wave to a left-handed one instead of a right-handed one. Alternatively, the direction of the current in the coil 36 may be reversed to invert the direction of the bias magnetic field applied to the ferrite rod 34, thereby changing only the sign of the Faraday rotation angle while keeping the absolute value unchanged. This allows the mode converter 5 to output a left-handed circularly polarized wave, or the direction of the current may be arbitrarily switched to selectively use right-handed and left-handed circular polarization.

[0044] In this embodiment, the plasma in the processing chamber 9 included in the load is magnetized, and therefore its dielectric constant is anisotropic. Generally, for such an anisotropic load, not only do the magnitude and phase of the load impedance vary depending on the polarization state of the incident microwave, including linear polarization and elliptically polarized waves, but the transition of the polarization state from the incident wave to the reflected wave may also behave differently from an isotropic load. However, for magnetized plasma with a magnetic field vector symmetrical with respect to the central axis of the processing chamber, when FW is right-handed circularly polarized, RW is left-handed circularly polarized, and when FW is left-handed circularly polarized, RW is right-handed circularly polarized, just as in the case of no magnetic field. In other words, the premise of this embodiment remains unchanged, and therefore the uniformity effect of this embodiment can also be obtained in an ECR plasma processing apparatus.

[0045] Further advantages of this embodiment include that there is virtually no response time because the system configuration is simple without using a feedback control system, and that there is no need for moving parts such as an electric field sensor for monitoring the axial ratio of the circularly polarized wave (an index of the degree of sense mixing) or an actuator for adjusting the characteristics of the mode converter 5.

[0046] 1...microwave source, 2...rectangular waveguide, 3...isolator, 4...matching box, 5...mode converter, 6...cylindrical waveguide, 7...cylindrical cavity, 8...microwave introduction window, 9...processing chamber, 10...wafer, 11...sample stage, 12...circulator, 13a, 13b...E corner, 14...E corner, 15...septum, 16...cylindrical waveguide, 32...square-to-circular converter, 33...Faraday rotator, 34...ferrite rod, 35...support, 36...coil, 37...cylindrical step waveguide, 38...quarter-wave plate, 39...cylindrical waveguide, FW...traveling wave, RW...reflected wave.

Claims

1. A plasma processing apparatus comprising: a processing chamber in which a sample is plasma-processed; a high-frequency power supply that supplies high-frequency microwave power via a matching unit; a magnetic field forming mechanism that forms a magnetic field in the processing chamber; and a sample stage on which the sample is placed; the plasma processing apparatus further comprises a septum polarizer that converts the microwaves propagated through a circulator into circularly polarized waves; a first port of the circulator is connected to the high-frequency power supply via the matching unit; a second port of the circulator is connected to one port of the septum polarizer via an impedance matching unit; and a third port of the circulator is connected to the other port of the septum polarizer via an impedance matching unit; the microwaves propagated to the one port are converted into right-handed circularly polarized waves, and the microwaves propagated to the other port are converted into left-handed circularly polarized waves; and the impedance matching unit comprises a rectangular waveguide. a width dimension of the rectangular waveguide and a length dimension of the rectangular waveguide that are defined so as to match impedance of the propagated microwaves; 2. The plasma processing apparatus according to claim 1, wherein ferrite is disposed in the waveguide of said circulator.

3. A plasma processing apparatus according to claim 1, wherein an electromagnet is disposed in the waveguide of said circulator.

4. A plasma processing apparatus according to claim 1, wherein the traveling wave propagated from said circulator is propagated to said one port.

5. A plasma processing apparatus according to claim 1, wherein the interior of said septum polarizer is separated by a metal septum.

6. The plasma processing apparatus according to claim 1, wherein the microwaves are microwaves of 2.45 GHz.

7. A plasma processing apparatus comprising a processing chamber in which a sample is plasma-processed, a high-frequency power supply that supplies microwave high-frequency power via a matcher, a magnetic field forming mechanism that forms a magnetic field in the processing chamber, and a sample stage on which the sample is placed, further comprising: a Faraday rotator that rotates the phase of the polarization plane of linearly polarized wave propagated through the matcher by (90 x n + 45) degrees, where n is an integer; and a waveguide-type circular polarization converter that switches between right-handed and left-handed circular polarization of the output circularly polarized wave every time the phase of the polarization plane of the linearly polarized wave rotated by the Faraday rotator changes by 90 degrees, wherein the waveguide-type circular polarization converter is disposed between the Faraday rotator and the processing chamber, and impedance is matched between the Faraday rotator and the waveguide-type circular polarization converter.

8. A plasma processing apparatus according to claim 7, wherein the Faraday rotator comprises a member made of garnet-type ferrite.

9. A plasma processing apparatus according to claim 7, wherein said Faraday rotator comprises a stepped cylindrical waveguide.

10. A plasma processing apparatus according to claim 7, wherein said waveguide type circular polarization converter is provided with a quarter wave plate.

11. A plasma processing apparatus according to claim 10, wherein the quarter-wave plate is a rectangular quartz plate having rectangular cutouts at the top and bottom in the direction of the long side.

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